The Mariners recalled Simpson from Triple-A Tacoma ahead of Sunday's game against the Twins.
Simpson has appeared in four games out of the Seattle bullpen this season, giving up three earned runs on four hits and two walks across three innings. He'll likely be in store for an abbreviated stay with the big club, as the Mariners will need to clear room on the 26-man active roster for the newly acquired Seranthony Dominguez prior to Tuesday's series opener with the Tigers.